Triethoxy(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)silane

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Bacterial mutagenicity: negative with and without metabolic activation in Salmonella typhimurium strains TA 98, TA 100, TA 1535 or TA 1537 (OECD 471) (Hüls, 1997).

Bacterial mutagenicity: read across from [2-(perfluorohexyl)ethyl]dichloro(methyl)silane (CAS 73609-36-6 ): negative with and without metabolic activation in Salmonella typhimurium strains TA 1535, TA 1537, TA 98, TA 100 and TA 102 (OECD 471) (LPT, 2002).

Mammalian cytogenicity: negative with and without metabolic activation in Chinese hamster V79 cells (OECD 473)(Eurofins Biopharma, 2016).

Mammalian mutagenicity: negative with and without metabolic activation in mouse lymphoma L5178Y cells (OECD 490) (Eurofins Biopharma, 2016).

The studies were conducted according to appropriate OECD test guidelines, and in compliance with GLP.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Additional information

[2-(Perfluorohexyl)ethyl]triethoxysilane has been tested for mutagenicity to bacteria, in a study which was conducted according to the OECD Guideline 471, compliant with GLP (Hüls, 1997). The range of strains does not comply with the current guideline. No evidence of a test-substance related increase in the number of revertants was observed in Salmonella typhimurium strains TA 98, TA 100, TA 1535 or TA 1537 when tested with or without metabolic activation in the initial plate incorporation assay or the repeat preincubation experiment up to cytotoxic/limit concentrations. Appropriate positive and solvent controls were included and gave the expected results. It is concluded that the test substance is negative for mutagenicity to bacteria under the conditions of the test.

No data are available for the mutagenicity of [2-(perfluorohexyl)ethyl]triethoxysilane in a strain of bacteria that can detect cross-linking mutagens, so data are read across from the related substance, [2-(perfluorohexyl)ethyl]dichloro(methyl)silane (CAS 73609-36-6), which has been tested in a reliable study, conducted according to OECD 471 and in compliance with GLP (LPT, 2002). No test-substance related increase in the number of revertants was observed with and without metabolic activation when tested up to cytotoxic concentration in Salmonella typhimurium strains TA 1535, TA 1537, TA 98, TA 100 and TA 102. The result of the initial plate incorporation assay was confirmed in an independent experiment using the pre-incubation method. Appropriate positive and solvent controls were included and gave expected results. It is concluded that the substance is negative for mutagenicity to bacteria under the conditions of the test.

[2-(Perfluorohexyl)ethyl]triethoxysilane has been tested for ability to cause chromosome aberrations in Chinese hamster V79 cells according to OECD TG 473 and in compliance with GLP (Eurofins BioPharma, 2016). No increase in the number of cells with aberrations was observed either with or without metabolic activation up to precipitating concentrations. Appropriate solvent, negative (treatment medium) and positive controls were included and gave the expected results. It is concluded that the test substance is negative for the induction of chromosome aberrations under the conditions of this study.

[2-(Perfluorohexyl)ethyl]triethoxysilane has been tested for mutagenicity in mouse lymphoma L5178Y cells according to OECD TG 490, and in compliance with GLP (Eurofins BioPharma, 2016). No test-substance induced increase in the number of mutations was observed when tested up to limit concentrations. Appropriate solvent, negative (treatment medium) and positive controls were included and gave expected results. It is concluded that the test substance is negative for mutagenicity to mammalian cells under the conditions of the study.

Read-across justification

Non-testing methods including read-across from surrogate substances are able to provide information on genetic toxicity (REACH Guidance part 07a, R.7.7.3). In the case of genetic toxicity the presence or absence of functional groups that are known to be related to genetic toxicity is considered important, as the presence or absence of reactive groups and molecular substructures is associated with mutagenic and carcinogenic properties of chemicals (Benigni and Bossa, 2006). Consideration is therefore given to the structural similarity, particularly presence or absence of structural alerts for genetic toxicity, when selecting surrogate substances for genetic toxicity endpoints. Additional information is given in a supporting report (PFA 2013aa).

Read-across hypothesis

The hypothesis is that that source (read-across) substances and registration (target) substance have similar systemic toxicological properties because they hydrolyse to similar silanol hydrolysis products, [2-(perfluorohexyl)ethyl]silanetriol and [2-(perfluorohexyl)ethyl]methylsilanediol and the non-silicon products, ethanol and hydrogen chloride. None of the substances or hydrolysis products have structural alerts for genetic toxicity. Based on publically available information, ethanol and hydrogen chloride are not known to contribute to toxicity at the relevant dose levels (OECD, 2004b and 2002), which is discussed further below.

The registered substance, [2-(perfluorohexyl)ethyl]triethoxysilane, hydrolyses at a moderate rate at neutral pH, and rapidly at low pH, with hydrolysis half-lives of approximately 3 hours at 37.5ºC and pH 7, and approximately 13 seconds at 37.5ºC and pH 2. The products of hydrolysis are [2-(perfluorohexyl)ethyl]silanetriol and ethanol.

The read-across substance, [2-(perfluorohexyl)ethyl]dichloro(methyl)silane, hydrolyses very rapidly, with a hydrolysis half-life of approximately 5 seconds at pH 2 and 25°C, at pH 7 and 37.5°C and at pH 2 and 37.5°C. The products of hydrolysis are [2-(perfluorohexyl)ethyl]methylsilanediol and hydrogen chloride.

Read-across justification

(a) Structural similarity of parent substance and silicon-containing hydrolysis products

[2-(perfluorohexyl)ethyl]triethoxysilane and [2-(perfluorohexyl)ethyl]dichloro(methyl)silane are both salines with highly (but not fully) fluorinated hexyl(ethyl) groups attached to the silicon; the registered substance has three ethoxy groups attached to the silicon, the read-across substance has two chlorine groups and one methyl group. Both hydrolyse rapidly to similar silicon-containing hydrolysis products, [2-(perfluorohexyl)ethyl]silanetriol and [2-(perfluorohexyl)ethyl]methylsilanediol. The other hydrolysis products, ethanol and hydrogen chloride, are not expected to contribute to genetic toxicity.

(b) Lack of structural alerts

None of the substances or hydrolysis products has structural alerts for genotoxicity (Benigni et al., 2008).

(c) Lack of genetic toxicity of the non-silicon hydrolysis product.

Hydrogen chloride gave negative results in the most reliable of the bacterial mutagenicity studies. Positive results were obtained in mutagenicity and cytogenicity assays using mammalian cells (OECD, 2002; ECHA disseminated dossier for hydrogen chloride). The positive results were associated with a decrease in pH, and it is considered that the positive results were likely to have been caused by reduced pH. Positive results caused by high or low pH effects are considered not to be relevant for in vivo situations (ECHA guidance Chapter R.07a), and testing should be carried out at neutral pH.

Ethanol is negative in Salmonella typhimurium bacterial mutagenicity assays, up to limit concentrations, including an appropriate 5th strain (TA 102). No evidence for cytogenicity was found in chromosome aberration studies using cultured human lymphocytes or Chinese hamster ovary cells. A mammalian mutagenicity assay using L5178Y cells gave negative results with and without metabolic activation. Ethanol did not induce micronuclei in bone marrow of rats, or chromosome aberrations in rats or hamsters. Ethanol was negative in the most reliable rodent dominant lethal assay (OECD, 2004b).

Benigni et al (2008).The Benigni/Bossa rule base for mutagenicity and carcinogenicity JR Scientific report EUR 23241 EN

OECD (2002): SIDS Initial Assessment Report for SIAM 15, Boston, USA, 22-25 October 2002: hydrogen chloride, CAS 7647-01-0.

OECD (2004b): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 19-22 October 2004, Ethanol, CAS 64-17-5.

Justification for classification or non-classification

Based on the available data for [2-(perfluorohexyl)ethyl]triethoxysilane, no classification is required for genetic toxicity according to Regulation (EC) No 1272/2008.